The present invention relates to a valve for controlling flow of hydraulic fluid. The valve is used to control the flow of hydraulic fluid to a power steering motor.
A known power steering control valve for controlling flow of hydraulic fluid to a power steering motor includes a hollow valve sleeve and a valve core. The core is positioned within the sleeve. The core and sleeve are relatively rotatable. Each of the core and sleeve has a plurality of lands and grooves.
When the spool and sleeve are in a neutral position fluid is communicated to opposite chambers of the power steering motor at equal pressures. When the core and sleeve are relatively rotated from the neutral position, fluid flow is variably restricted. Restriction of the fluid flow causes pressurized fluid to be delivered to one of two chambers of a hydraulic power assist motor to cause motor actuation.
The restriction is provided by lands on the core and sleeve which radially overlap to define narrow flow gaps. Variation of the flow gap, and the amount of restriction, is provided by end surface segments of the lands which are formed such that varied amounts of relative rotation between the core and sleeve cause the overlapping end surface segments to be positioned at varying distances apart. Due to high volume of hydraulic fluid flow and pressure differential changes (drops) as the hydraulic fluid flows through the flow gaps, the control valve creates noise. The noise includes noise due to cavitation created by fluid flowing through a gradually expanding flow area.